A new study concludes that sounds unrelated to a listener’s immediate task – otherwise known as “distractions” – can hurt cognitive performance.

The Louisiana State University research appears to provide yet more evidence that multitasking – engaging in multiple activities simultaneously – diminishes a person’s focus and productivity.

In four separate experiments, both local second-graders and LSU psychology students were shown words on a computer screen and instructed to remember them in the correct sequence. As the participants read the words, they also sometimes heard unrelated words in the headphones all were wearing.

Adults in the LSU study showed a word recall performance drop of 10% on average, while the second-graders’ performance diminished by up to 30% on average.

In other words, cognitive processing by study participants was impaired when they were distracted by competing stimuli, which reduced their ability to perform required jobs (in this case, reading and memorizing).

“The research that I have done and that I have read indicates that multitasking comes at a price, even though the person may be unaware. The costs are typically shown in an overall slower time to finish a task, and/or increased rate of errors.”

Multitasking has been studied for years, even before the widespread adoption of personal digital devices and the Internet. Research invariably shows that the processes of switching between tasks (going from email to a spreadsheet, for example) and trying to absorb competing streams of information (reading while watching YouTube videos or driving while texting) impairs the brain’s ability to absorb and evaluate information, thus reducing overall productivity and increasing the changes of error.

In the case of texting and driving, the results can be deadly. In the workplace, the downside of multitasking is diminished effectiveness and waste. A 2010 study by Workplace Options, an employee-support services organization, estimated that multitasking costs U.S. businesses $650 billion a year in lost productivity through distractions.

Multitasking is becoming a hot topic in the enterprise world as millions of workers not only bring personal devices into the office, but also tap into a widening variety of social media.

In response, a small industry has grown around the notion of “mindfulness,” or teaching employees to be more effective in their jobs by learning to concentrate and eliminate distractions.

Despite the overwhelming body of research, not to mention plain common sense, many people argue that multitasking actually increases their effectiveness, and that younger professionals especially – the “Millennials” – are “wired differently than those above 35 years of age,” as this Mobilize.org blogger writes.

That last “fact” will come as a surprise to some neuroscientists, since changes to the brain tend to take a bit more time than, say, one generation. And even if “wired differently” merely means Millennials are better able to adapt to a multitasking world, well, the research just doesn’t support that.

That being said, recent research described in Psychology Today shows that 2% of people – “supertaskers” -- have the ability to perform multiple tasks without their performance suffering.

David Strayer, director of the applied cognition lab at the University of Utah, told Psychology Today that supertaskers actually do have different brain structures than the other 98% of people:

“These brain regions that differentiate supertaskers from the rest of the population are the same regions that are most different between humans and nonhuman primates.”

Great news for our supertasking overlords, if not for rest of us. And since evolution isn’t likely to help us catch up over the span of, say, a smartphone product cycle, we probably should adjust our work habits to accommodate our humbling limitations.